1. Field of the Invention
The present invention relates to disc grinders, such as hand-held disc grinders, used for grinding stone or the any other materials.
2. Description of the Related Art
In general, hand-held electric disc grinders have a substantially cylindrical body section and an electric motor disposed within the body section. In order to perform a grinding operation, the user may grasp the body section, so that the body section serves as a grip member. One the front side of the body section, there is disposed a reduction gear section including a bevel gear train that reduces the rotation of the electric motor and transmits the rotational output in a direction perpendicular to the motor axis. Therefore, a spindle disposed on an output side of the reduction gear mechanism extends perpendicular to the motor axis. A circular grinding wheel is mounted to a front end of the spindle. Substantially rear half of the circumference (on the side of the user) of the grinding wheel is covered by a grinding wheel cover for preventing ground powder or the like produced during the grinding operation (hereinafter simply called powder dust) from scattering toward the side of the user.
For the convenience of the operation for exchanging the grinding wheel or any other operation, the grinding wheel cover is configured to be detachable. In addition, the position of the grinding wheel cover about the rotational axis of the spindle can be changed, so that the position of covering the grinding wheel can be changed in accordance with the posture of the user during the operation. Typically, the grinding wheel cover has an annular mounting band portion that can be mounted to a cylindrical boss portion of the reduction gear section and can be fastened thereto by tightening a fixing screw. Therefore, loosening the fixing screw can release the mounting band portion for removing the grinding wheel cover or for changing the position of the grinding wheel cover,
In the case of the grinding wheel cover having the mounting structure as described above, the powder dust may scatter to the side of the user if the user adjusts the grinding wheel cover unintentionally to a position where the grinding wheel cover is opened by a large angle toward the user. Therefore, in some cases, the structure enabling adjustment to a desired position has invited an undesired situation from a viewpoint of preventing the powder dust from scattering.
In addition, if the fixing screw has not been sufficiently tightened, it may be possible that the position of the grinding wheel cover is shifted toward an open position, for example, in the case that the grinding wheel cover contacts an object to be ground. In such a case, the function of preventing the powder dust from scattering may not be sufficiently performed.
In order to solve the above problem, US2010/0210195A (corresponding to International Publication No. WO2009/054275) has proposed to provide a stopper projection on a mounting band portion of a grinding wheel cover and to provided a stopper contact portion on the side of a reduction gear section, so that the grinding wheel cover is prevented from rotating further after the stopper projection has contacted the stopper contact portion. Therefore, the position adjustable range of the grinding wheel cover is limited within a predetermined angular range. With this technique, it is possible to avoid such an occasion that the user unintentionally adjusts the position of the grinding wheel cover by a large angle more than necessary. In addition, it is possible to maintain the grinding wheel cover within an adequate angular range even in the case that the grinding wheel cover has contacted an object to be ground. Therefore, the function of preventing the powder dust from scattering toward the user can be reliably preformed.
However, the grinding wheel cover of the above publication has still required an improvement. In the case of the technique of the above publication, the position adjustable range of the grinding wheel cover is limited within a predetermined angular range through contact of the stopper projection on the side of the grinding wheel cover with the stopper contact portion on the side of the reduction gear section. However, if the grinding wheel cover contacts an object to be ground with a strong impact force, the stopper projection may contact the stopper contact portion also with a strong impact force.
Therefore, there has been a need in the art to improve the durability of the grinding wheel cover against the impact force.